The invention pertains to a coated cutting insert with a coating scheme and a method for making the same wherein the coating scheme includes a coating layer of titanium oxycarbonitride. More specifically, the invention pertains to a coated cutting insert (wherein the substrate may be polycrystalline cubic boron nitride (PcBN)) with a coating scheme and a method for making the same wherein the coating scheme includes a coating layer of titanium oxycarbonitride deposited by chemical vapor deposition (CVD) from a gaseous mixture including acetonitrile, especially acetonitrile in an amount not greater than about 0.15 Mole percent of the gaseous mixture. Further, the invention pertains to a coated cutting insert (wherein the substrate may be polycrystalline cubic boron nitride (PcBN)) with a coating scheme includes a coating layer of titanium oxycarbonitride applied by CVD wherein the titanium oxycarbonitride whiskers have, as measured in the two-dimensional plane view per the technique set forth hereinafter, an average length greater than about 1.0 μm, an average width greater than about 0.2 μm, and an average aspect ratio greater than about 2.0.
Heretofore, acetonitrile (CH3CN) has been used in a gaseous mixture to deposit via CVD a coating layer. U.S. Pat. No. 7,455,918 to Gates, Jr. et al. lists a number of gaseous compositions, which include acetonitrile, that can be used to deposit a modification layer comprising multiple layers including titanium oxycarbonitride. See Col. 6, lines 48-67. Specific examples are set forth in Table 5 and Table 6 of U.S. Pat. No. 7,455,918 to Gates, Jr. et al. that include an undisclosed volume of acetonitrile in a gaseous mixture of hydrogen, nitrogen, titanium tetrachloride, and carbon monoxide. European Patent No. 1 413 648 B1 to Sumitomo Electric Industries, Ltd. appears to show the use of CH3CN along with other gases to produce a columnar structure which possibly could be TiOCN. See page 3, line 48 through page 4, line 5. The other gases appear to include ones selected from VCl4, ZrCl4, TiCl4, H2, N2, Ar, CO, and CO2. It appears the gaseous mixture requires the presence of H2O. Table I (page 8) sets out examples that use from 0.3 to 2.0 volume percent acetonitrile to form the TiCNO coating layer.
For some time, acetonitrile has been a part of a gaseous mixture used to deposit via CVD a coating layer of titanium carbonitride, as well as other coating layers. In this respect, PCT Patent Publication WO 00/52224 to Undercoffer (assigned to Kennametal Inc.) apparently discloses at page 2, line 12 through page 3, line 11 that acetonitrile (along with other gases (e.g., TiCl4 and H2)) has been used in the deposition of titanium carbonitride, which seems to be the focus of PCT Patent Publication WO 00/52224. At page 11, lines 4-12, PCT Patent Publication WO 00/52224 mentions that adding CO or CO2 to the gaseous mixture may result in the production of other titanium-containing coatings including titanium oxycarbonitride (TiOCN).
United States Patent Application Publication No. US2007/0298280 to Omori et al. discloses the use of acetonitrile to deposit a coating layer of titanium carbonitride. There is a general mention about the use of acetonitrile to deposit via CVD a titanium oxycarbonitride coating layer. See Paragraphs [0057] through [0060]. European Patent Application No. 1 138,800 A1 to Kodama et al. focuses on the use of ethane in the production of a hard coating that includes titanium oxycarbonitride. However, there is a mention that one could use acetonitrile in place of ethane in the process. See Paragraphs [0021]-[0024].
European Patent Application No. 1160 353 A1 to Hirakawa et al. discloses a TiCN layer with a concentration gradient wherein the CH3CN concentration in the gas mixture is one of the factors that impacts the TiCN concentration. In the examples, the TiOCN layer does not use CH3CN as a component of the gaseous mixture.
United States Patent Application Publication No. US2006/0115662 to Ruppi discloses the use of CH3CN to make a titanium aluminum oxycarbonitride coating “bonding” layer. See Table I and Table II. United States Patent Application Publication No. US2006/0257689 A1 to Sottke et al. discloses the use of acetonitrile (0.5-2 vol. %) in the deposition of an intermediate layer that could be TiOCN with the Ti replaced at least to some extent by Zr or Hf. U.S. Pat. No. 7,192,660 B2 to Ruppi contains a disclosure that alludes to using CH3CN to produce a (Tix, Aly, XZ)(Cu,Ow,Nv) coating layer wherein x, u and v are greater than zero and at last one of y, z and w is greater than zero. See Col. 5. lines 53-63.
The following patent documents use acetonitrile in the gaseous mixture to deposit a titanium carbonitride coating layer: European Patent No. 0 732 423 B1 to Moriguchi et al., European Patent No. 1 188 504 to Kato et al., European Patent Application No. 0 900 860 A2 to Ichikawa et al., U.S. Pat. No. 5,681,651 to Yoshimura et al., U.S. Pat. No. 5,915,162 to Uchino et al., U.S. Pat. No. 6,436,519 B2 to Holzschuh, European Patent No. 0 685 572 B1 to Mitsubishi Materials, European Patent No. 1 157 143 B1 Kennametal Inc., and European Patent No. 0 709 484 B1 to Mitsubishi Materials.
Adhesion of the coating scheme to the substrate is an important feature for a coated cutting insert. A coating scheme that has improved adhesion is beneficial to performance. Thus, it would be highly desirable to provide a coated cutting insert that experiences improved adhesion of the coating scheme to the substrate.
In some coating schemes for use with a coated cutting insert, an alumina coating layer is joined to a moderate temperature titanium carbonitride (MT-TiCN) coating layer via a bonding layer. Applicants have discovered that by using a titanium oxycarbonitride coating layer as the bonding layer, which exhibits elongate whiskers of titanium oxycarbonitride with certain dimensions and aspect ratios, there is an improvement in the adhesion of the alumina coating layer as compared to a bonding layer of titanium carbonitride. Thus, it would be highly desirable to provide a coated cutting insert with a coating scheme including titanium oxycarbonitride that provides improved adhesion. Further, it would be highly desirable to provide a coated cutting insert with a coating scheme including titanium oxycarbonitride that provides improved adhesion wherein the titanium oxycarbonitride whiskers have certain dimensions and aspect ratios that facilitate improved adhesion.
In order to achieve the coating layer of titanium oxycarbonitride wherein titanium oxycarbonitride whiskers have, as measured in the two-dimensional plane view per the technique set forth hereinafter, an average length greater than about 1.0 μM, an average width greater than about 0.2 μm, and an average aspect ratio greater than about 2.0, applicants have used a reduced amount of acetonitrile in the gaseous mixture used to deposit the titanium oxycarbonitride coating layer. Applicants have found that the maximum amount of acetonitrile in the gaseous mixture should not be greater than about 0.15 Mol percent of the gaseous mixture. Thus, it would be highly desirable to provide a coated cutting insert with a coating scheme including a titanium oxycarbonitride coating layer wherein the gaseous mixture used to deposit the titanium oxycarbonitride coating layer has a reduced content (i.e., not greater than about 0.15 Mol percent of the gaseous mixture) of acetonitrile.
Applicants have found that there is an advantage to a titanium oxycarbonitride bonding layer, which improves the adherence of the alumina coating layer, at a lower CVD deposition temperature. This is especially true for the CVD deposition of the titanium oxycarbonitride layer on a substrate of polycrystalline cubic boron nitride (PcBN). The PcBN substrate can degrade upon the CVD deposition of the titanium oxycarbonitride layer at too high of a deposition temperature. The lower deposition temperature is below about 1000° C. In one alternative, the CVD deposition temperature is between about 800° C. and about 950° C. In another alternative, the CVD deposition temperature is between about 895° C. and about 925° C.